Evidence for the existence of embryonic diapause in the domestic-introduced subtropical stick insect, Entoria okinawaensis (Phasmatodea: Phasmatidae)

Entoria okinawaensis Shiraki, 1935 (Phasmatodea: Phasmatidae) is a stick insect originally distributed among the subtropical islands of Japan. This species, after introduction into the southernmost regions of Kyushu Island, became established there. After insects were collected for this study from Ibusuki city, Kagoshima prefecture, Japan, their eggs were used for experimentation. Embryonic development was fundamentally temperature dependent. At 25 °C, many eggs hatched approximately 2 months after oviposition. However, hatching was observed continuously until the end of the 240-day experiment. Findings from egg dissection suggest that a small number of eggs arrest development at the early embryonic stages. Fluorescence observation of DAPI-stained eggs reveals that eggs show arrested development at the very attenuated blastoderm period. This study proves the existence of embryonic diapause in E. okinawaensis, although the incidence of diapause eggs is small. If future changes in the incidence and duration of diapause as adaptations to local climate occur, then the domestic-introduced subtropical stick insect might expand its distribution range farther north.